Both bluetooth (BT) and wireless local area network (WLAN) devices generally operate in 2.4 GHz band. Thus, BT and WLAN signals are likely to interfere onto each other when the BT and WLAN devices are co-localized, where co-localization of the devices may entail using the same antenna or being located in the same circuit board, chip, or apparatus. For example, the BT device which is in receiver mode may be blinded or saturated due to the transmission by the WLAN device. Although the receiver of the BT device is designed to receive a signal directed to the BT device, the power spilled from the WLAN device may be high enough to desensitize the receiver of the BT device due to their proximity to each other.
Several solutions are on the market to limit the interference between the BT and WLAN devices. Adaptive frequency hopping (AFH), which is one of the solutions, is a technique used by the BT device to modify its hopping pattern based on frequency bands not occupied by other devices, such as the WLAN device. The AFH aims at avoiding a subset of BT frequencies occupied by the WLAN device during the BT frequency hopping process. The BT device either discovers or is informed which band to jump during the AFH. Alternatively, hardware shutdown of the BT device and/or WLAN device can be implemented to protect ongoing reception by either device. To execute the shutdown, a signal or signals can be exchanged between the BT device and the WLAN device using their pin connections. For example, the WLAN device can be told to shut down its transmission when the BT device is in receiver mode or vice versa.
However, the AFH may not work so well when the BT device is co-localized with the WLAN device. Since the AFH works satisfactorily only when the BT device is able to determine whether the signal received by its antenna is in a frequency band which can be used for hopping, the BT device, with its receiver desensitized due to strong transmission signal from the co-localized WLAN device, may not be able to make that decision.
The hardware shutdown may not be so effective for either of the co-localized devices. For example, the WLAN device may need to send an acknowledgement signal to a peer WLAN device when it receives a packet from the peer WLAN device, during which time, if the BT device is in receiver mode, the WLAN device may be prevented from transmitting the acknowledgement signal. When the BT reception session is prolonged, the peer WLAN device would keep sending the same packet repeatedly until it gets the acknowledgement from the WLAN device. This may lead to a physical layer (PHY) rate decrease and hence longer frame duration. This also may lead to higher collision probability between signals of the BT device and the WLAN device. Moreover, if the BT reception session is maintained long enough, the peer WLAN device may drop the WLAN device from its communication link, thinking that the link has been degraded. This in turn may result in loss of data intended for the WLAN device.